您如何模仿描述输出? [英] How can you mimic the description output?

问题描述

想象一堂水果:

class Fruit: NSObject {
    override var description:String {
        return super.description
    }
}

var apple = Fruit()
var banana = Fruit()

print(apple)  // Output: <MyProject.Fruit: 0x7fa719627e00>
print(banana) // Output: <MyProject.Fruit: 0x7fa71962dab0>

问题:您如何模仿此输出?

我目前有以下内容:

class Fruit: NSObject {
    override var description:String {
        print(super.description)
        return "<\(NSStringFromClass(self.dynamicType)): 0x\(String(self.hash, radix:16))>"
    }
}

现在输出以下内容:

<MyProject.Fruit: 0x7fb958c289a0>
<MyProject.Fruit: 0x7fb958c289a0>
<MyProject.Fruit: 0x7fb958c22df0>
<MyProject.Fruit: 0x7fb958c22df0>

如您所见，输出是相同的，这正是我想要的.现在我想知道这是否是模仿其输出的正确方法，还是我忽略了下面评论中提到的内容.

As you can see the output is the same which is what I wanted. Now I am wondering if this is the proper way to mimic it's output or that I am overlooking something as mentioned in the comments below.

信用:Matt，Martin R和Vacawama

推荐答案

NSObject的任何子类都继承了

Any subclass of NSObject inherits the description method of NSObject (which is defined in the NSObjectProtocol):

class Foo1 : NSObject { }
print(Foo1())
// <MyProject.Foo1: 0x100612fd0>

此默认实现"打印类名和内存 对象的地址，例如 星期五问答，2013-01-25:生成NSObject ，其中显示了Objective-C实现的方式 可能像这样:

This "default implementation" prints the class name and the memory address of the object, see for example Friday Q&A 2013-01-25: Let's Build NSObject, where it is shown how the Objective-C implementation could look like:

- (NSString *)description
{
    return [NSString stringWithFormat: @"<%@: %p>", [self class], self];
}

%p格式将指针的值打印为十六进制数字， 在0x之前.

The %p format prints the value of a pointer as a hexadecimal number, preceded by 0x.

要模仿在Swift中，我们可以使用

To mimic that in Swift, we can use

• String(reflecting: self.dynamicType)，它以字符串形式返回完全限定的类名，并且
• unsafeAddressOf(self)，它返回指向存储的指针 对象.

• String(reflecting: self.dynamicType) which returns the fully-qualified class name as a string, and
• unsafeAddressOf(self) which returns a pointer to the storage of the object.

示例(使用方括号[]演示 使用覆盖的方法):

Example (using square brackets [] to demonstrate that the overridden method is used):

class Foo2 : NSObject {
    override var description : String {
        let className = String(reflecting: self.dynamicType)
        let address = unsafeAddressOf(self)
        return String(format: "[%@: %p]", className, address)
    }
}
print(Foo2())
// [MyProject.Foo2: 0x100613310]

class Foo3 : Foo2 { }
print(Foo3())
// [MyProject.Foo3: 0x102000540]

这也适用于纯Swift类"，因为没有Foundation 使用的方法:

This works for "pure Swift classes" as well, because no Foundation methods are used:

class Bar : CustomStringConvertible {
    var description : String {
        let className = String(reflecting: self.dynamicType)
        let address = unsafeAddressOf(self)
        return String(format: "[%@: %p]", className, address)
    }
}
print(Bar())
// [MyProject.Bar: 0x102001200]

请注意(如以上注释中所述)，哈希值 对象的地址不一定与存储器地址相同. 一个简单的示例是NSArray()，其哈希值仅是数字 元素:

Note that (as already mentioned in above comments), the hash value of an object is not necessarily identical to the memory address. A simple example is NSArray() whose hash value is just the number of elements:

let array = NSArray(objects: 1, 2, 3)
print(unsafeAddressOf(array)) // 0x00000001020011a0
print(array.hashValue) // 3

---

针对Swift 3的更新

class Bar : CustomStringConvertible {
    var description : String {
        let className = String(reflecting: type(of: self))
        let address = Unmanaged.passUnretained(self).toOpaque()
        return "[\(className): \(address)]"
    }
}

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